Ken Moore wrote this article about controlling broom in California. French broom (Genista monspessulana), Spanish broom (Spartia junceum) and Scotch broom (Cytisus scoparius) are invasive plants throughout California. However, the article offers advice for the long-term control of a variety of invasive species. Ken originally wrote this article for the California Invasive Plant Council Newsletter. We reprint it here with permission.
Ken started working on invasive species control in 1963! He started the Wildlands Restoration Team in 1990. Go to the website for some great articles on invasive species control techniques. Also, here is a video of a short interview with Ken Moore. G
In analytic geometry, an
Fig. 1 Deer Herbivory
asymptote of a curve is a line such that the distance between the curve and the line continually approaches closer to, but never quite achieves zero as they tend to infinity.
It is a universally relevant principle, with applications in such diverse fields as quantum mechanics, particle theory, hierarchical resemblance; even philosophy. As you approach infinity (completion, perfection, etc.) each further step becomes disproportionally more difficult.
Examples abound: Sharpening weed tools is easy. But to obtain the edge a surgeons’ scalpel requires honing with successively finer stones, followed by polishing with successively finer rouges. However, even that mirror edge looks rough under a microscope, because the finest abrasives still cannot produce the theoretically perfect, sharpest edge.
In weed work where eradication is the goal, infinity = zero presence. This is always challenging, but broom, more than anything else I’ve tackled, epitomizes the asymptote principle. Broom control has three distinct phases:
PHASE 1 is removal of standing broom. Everything from hands to heavy equipment is employed at this stage. While this appears to be the hardest step, it’s actually the easiest, even though it’s the most work! People love the satisfaction they get from visible results.
PHASE 2 Broom removal has triggered the seedbank, and you’re faced with a sea of seedlings. Now the real difficulty of controlling broom becomes apparent. People don’t relish pulling endless seedlings. Where they can be used, flaming and foliar spray are the major methods employed on larger sites. But after a few years, native plant growth on most sites will preclude using either of these methods. You’ve entered…
PHASE 3. Native plants have achieved sufficient size and density so that broom is getting harder to see each year. Hand pulling or stem treatments are required now, and even seasoned pullers are missing broom. You’re close to finishing, yet it’s harder to prevent seed set. The asymptote principle! Paul Simon put it succinctly: “The nearer your destination, the more you slip-sliding away.”
However, there are forces gathering out there which have taken me 25 years to fully appreciate. Their effects are only beginning to become visibly apparent, and are therefore under-valued by many land managers.
Broom cannot tolerate heavy shade. It usually established following logging or other activities that removed tree canopy. Now that these areas are recovering, broom is increasingly shaded out. And where we’re boosting native re-growth by removing broom, the effect is dramatic. Check seed pods in shady areas. They may still form, but not reach maturity.
Evolution is also helping. Yep, even on broom sites! When broom initially established here, browsers
Fig. 2 Cambium Gnawing
probably ignored it. But sooner or later, one gets curious: “Hmmm, not bad.” The word gets around!
Deer, rabbits, squirrels, gophers, wood rats, mice, and voles have all benefitted from our removing many of their predators. There are more hungry mouths to feed out there, especially herbivores: Being nature’s larder on the hoof, they multiply copiously!
Not only are there more mouths, there’s less native forage available to them. As we “convert” natural areas and invasive species displace natives, those mouths will increasingly turn to non-native plants to survive.
But evolution doesn’t manifest itself overnight, so it’s no wonder that early signs of adaptation to broom by browsers go unnoticed. On sites where broom removal is not underway, it’s easy to miss. But look closely and you’ll see it, even there.
Where broom is being controlled, the effects of browsing escalate. As fewer plants remain, they get hammered even harder. This is particularly helpful in Phase 3, when plants are harder to find. And those hungry mouths are out there, 24/7!
Here’s what to look for: Check smaller broom around the edges of infestations. Deer nip off the tender ends of young plants, making a sharp angled cut. Fig. 1. Further in, wood rats, rabbits, mice, and voles gnaw the tender cambium layer, eventually girdling the stem. Fig. 2. Gophers and ground squirrels work mostly underground. They will completely sever the roots of large broom. I’ve seen entire stands of broom die in this way. Fig. 3.
Compounding all of this, there are many more of us out there, as well! Some 150 people attended our
Fig. 3 Root Herbivory
initial gathering in 1992, and I clearly remember we all wondered if we could ever assemble that number again. CalIPC is now 1,000 strong, and counting!
Still feeling these factors aren’t significant? Think longer term, when escalation of these combined processes has kicked in! Browsers may not eradicate broom alone, but they aren’t alone! Seeing them closing ranks behind us is empowering to me. The best ally we could ever have is the very one we’re working to save.
